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Pre-Eocene Synmetamorphic Structure in the Mindoro-Romblon-Palawan Area, West Philippines, and implications for the history of southeast Asia

Abstract : The structure of the pre-Eocene rocks, considered as the "basement" of the Philippines, has been investigated in the Mindoro-Lubang, Romblon-Tablas-Sibuyan, and North Palawan areas. In the former two areas the same pre-Eocene succession of units is recognized from top to bottom: (1) a pre-Eocene olistostrome; (2) an ophiolitic nappe; (3) a schistose sequence (pelites, sandstones, basic schists and marbles); and (4) a gneissic unit. The nature of the contact between the olistostrome and the underlying units is unclear, but the ophiolite and the schistose sequence form two thrust sheets of oceanic origin thrust upon the gneissic unit that is considered a part of a continental basement called the West Philippines Block. Small-scale structures show that the early deformation stage is characterized by a submeridian (0°-N40°E) lineation formed in greenschist to amphibolite facies conditions during the thrusting. Kinematic analysis show that the thrusting was from north to south. In North Palawan, metamorphic rocks with similar microtectonic and kinematic characteristics are found. They are overlain by a Late Jurassic olistostrome which is correlated with the olistostromes found in Calamian, North Mindoro, Carabao, and Buruanga peninsula (North Panay). The microstructural features and the presence of the olistostrome suggest that the North Palawan, Mindoro, Tablas, Romblon, Sibuyan, and Carabao islands belong to the same North Palawan block of Hamilton (1979) which is a continental fragment rifted from Asia in Cenozoic times. It is assumed that the Western Panay and Zamboanga areas, which are characterized by Mesozoic ophiolites and metamorphic rocks, also belong to the North Palawan Block. All these islands experienced, to some extent, the same Mesozoic geohistory: the south verging thrusting is interpreted as the result of an oblique collision of the West Philippines Block with Asia. The contemporaneous left-lateral strike-slip faulting and the calc-alkaline magmatism widespread along the Chinese margin are also included in the geodynamic model.
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Michel Faure, Yves Marchadier, Claude Rangin. Pre-Eocene Synmetamorphic Structure in the Mindoro-Romblon-Palawan Area, West Philippines, and implications for the history of southeast Asia. Tectonics, American Geophysical Union (AGU), 1989, 8 (5), pp.963-979. ⟨10.1029/TC008i005p00963⟩. ⟨insu-00716213⟩

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